1. Field of the Invention
This invention relates to a motor speed control apparatus; more particularly, this invention relates to an apparatus which has a motor, a frequency generator for generating a detective frequency signal proportional to the rotational speed of the motor, and a control signal generator for generating a control voltage signal which corresponds to the rotational speed-error of the motor for the reference frequency signal.
2. Description of the Prior Art
In a prior art systems, phase-controlled motor is widely used in order to stably control the rotational speed of the motor used, for example, for a record player. An advantage of the phase-controlled motor is that the motor rotates very accurately by using a stable frequency signal generated by a crystal oscillator or the like, and used for the reference frequency. Accordingly, the motor rotates very stably and uniformly for any load torque.
However, the phase-controlled motor comprises two loops, i.e. a speed feedback loop and a phase locked loop, and the construction of the phase-controlled motor is complicated, so that it is difficult to design the phase-controlled motor, and it is also bothersome to adjust it. In addition, these two loops interact with each other, and the motor suffers a bad effect from the interaction of these two loops, and it takes a long time to lock the motor, when the motor starts rotating.
Furthermore, according to a conventional phase-locked motor, the action points of these two loops are varied and the lock range of the motor is reduced because of the influence of ambient temperature changes or long term characteristic variations of the electronic components utilized.